Filter elements in use have cylindrical filter bags, mounted onto cylindrical wire cages, which are installed by means of snap-ring fittings in the housing. Air is drawn through the filter bags during the filtration process. In pulse-jet filter applications, the air flow direction is reversed during the cleaning cycle.
The filter bags are closed on the bottom and open on the top. The dust laden air is drawn through the filter bag from an exterior of the filter bag, and the dust particles are retained on the surface of the filter bag. The air-to-cloth ratio, dust particle size, electrostatic properties of dust and filter cloth, can velocity, dust retention and cake-release of a given filter material and the filtration surface texture determine the efficiency of a filter. Pulse-jet filter bags are limited by the length and circumference of the filter bags and the can velocity due to the small open space between the circular filter bags hanging in the bag house. Improving efficiency by increasing the size of the filter housing, or increasing the number of filter bags, is expensive and is often impractical. The circular, sewed-on bottoms often protrude beyond the sides of the bags of the filter elements and become obstacles that catch and collect dust, which later impedes dust release in the cleaning cycle, and creates a negative impact on the can velocity at the bottom of the filter elements.
Similarly, cartridge filters have the disadvantage of being limited in temperature resistance and in length, which typically may not exceed two meters. High differential pressure causes the pleats to concave at the tips of the pleats, thereby reducing the effective filter area at this point. In addition, dust and other undesirable particles build up on the outside between the pleats and, in some cases, completely clog the cartridge filter. The extruding rim of the bottom plate of the cartridge filter is frequently an obstacle that catches and retains dust, preventing the collected dust from falling down into the hopper.